(a) Field of the Invention
The present invention relates to a method of preparing mono-iodo benzene with a transiodination reaction, and more specifically to a method of preparing mono-iodo benzene by using multi-iodo benzene of a by-product produced in oxy-iodination.
(b) Description of the Related Art
An oxy-iodination reaction that synthesizes iodobenzene starting from benzene and iodine is carried out slowly, and thus is usually in liquid phase in the presence of an oxidative agent such as nitric acid, acetic acid, hydrogen peroxide, or silver sulfide.
The oxy-iodination reaction has been described in JP S58-077830 A, U.S.S.R. 453392, the Journal of the American Chemical Society, Vol. 39, page 437, 1917,etc.
In the oxy-iodination reaction, other oxidizing agents including iodic acid (HIO3), sulfur trioxide (SO3), and hydrogen peroxide (H2O2) have also been suggested, but none of these have proven to be more efficient than nitric acid.
The iodination reaction using metal halogenides as catalysts instead of an oxidizing agent is disclosed in the Bulletin of Chemical Society of Japan, Vol. 47, page 147, 1974. In the JP S57-077631 A, benzene is directly iodinated in gaseous phase by using 13X-type zeolite.
JP S59-219241 A suggested that an iodobenzene compound was produced from benzene by using a very acidic zeolite catalyst having a molar ratio of silicon to aluminum (Si/Al) of greater than 10 with oxy-iodination in an oxygen atmosphere.
EP0181790B and EP0183579B disclose methods for the synthesis of iodobenzene by oxidative iodination in a gaseous phase starting from benzene, iodine, and oxygen in the presence of air or other oxygen-containing gas with a zeolite catalyst. EP0181790B discloses zeolite catalysts of ZSM-5 type and ZSM-11 type that have been exchanged with divalent or trivalent cations prior to use. EP 0183579B suggested X-type or Y-type zeolite in non-acidic form to prevent inactivation of the catalyst, and the X-type or Y-type zeolite has to be used in a form in which it is exchanged with monovalent, divalent, or trivalent cations, and in particular, an alkaline metal or rare earth metal. In the methods of EP0181790B and EP0183579B, mono-iodo benzene (MIB) is produced with selectivity of higher than 90%, and only distinctly minor amounts of di-iodo benzene (DIB) compounds are produced as by-products.
As noted above, in the conventional methods, an iodinated aromatic compound is synthesized selectively with oxy-iodination. As shown in Reaction schemes 1 to 3, however, the oxy-iodination produces various iodinated aromatic compounds and undesired iodinated aromatic compounds as by-products.2C6H6+I2+O2—>2C6H5I+H2O   [Reaction Scheme 1]2C6H5I+I2+O2—>2C6H4I2+H2O   [Reaction Scheme 2]2C6H5I2+I2+O2—>2C6H3I3+H2O   [Reaction Scheme 3]
Because iodine is very expensive, the by-products of iodinated aromatic compounds are produced disadvantageously. Thus, iodine-containing by-products except MIB and p-DIB are required to convert to MIB and p-DIB with transiodination.
The transiodination method of iodinated aromatic compounds has been disclosed in U.S. Pat. Nos. 4,792,641, 4,806,698, 4,808,759 and 4,822,929. U.S. Pat. No. 4,792,641 discloses a method of transiodination of aromatic compounds, particularly DIB in a gaseous phase at 275˜500° C. with a non-acidic zeolite catalyst of an X type that is exchanged with an alkaline metal or alkaline earth metal prior to use. U.S. Pat. No. 4,806,698 disclose a method of transiodination of aromatic compounds, particularly iodonaphthalene, in a liquid phase at 180˜250° C. with acidic zeolite of an X-type, Y-type, or L-type. The methods have a disadvantage of serious inactivation of the catalyst, because iodonaphthalene is only used without a diluting agent such as benzene naphthalene.
EP 4808759B discloses a method of transiodination of polyiodobenzene, particularly DIB, at 250˜450° C. in the presence of benzene and oxygen with zeolites of an X or Y type exchanged with an alkaline metal or rare earth metal. EP 4822929B discloses a method of transiodination of polyiodobenzene, particularly DIB, with pentacyl zeolite exchanged with cations of a group II metal, a group III metal, or a group IV metal.
In most of the conventional methods, zeolites of X, Y, L, or ZSM-5 types in non-acidic form are used. In addition, the reaction conditions such as reaction temperature and reactant composition are different depending on the kinds of aromatic compounds such as benzene and naphthalene, but this has not been studied sufficiently. In particular, a method of increasing the selectivity of product and the stability of catalyst needs to be further studied.